Php - clear PNG metadata but keep similar quality - php

I want to convert every uploaded image to png. I think gd is a good approach for that, because it drops the metadata of the images, and does not try to parse it. I read that ImageMagick maybe has malware vulnerability on some linux servers...
I have 2 questions:
Does gd drop the PNG metadata too if the original file was PNG, or should I use pngcrush after converting?
Do I have the same quality loss as by saving JPEG files, or is the PNG format much better?


If you would open the png in PHP, copy it to a new resource, then save it at full quality (in PNG, JPEG will lose quality) it will do what you want.

Related

Load image faster

lately, I'm searching about optimizing heavily loaded sites with a lot of images and I found this to optimize images:
resizing image
compressing image
and using CDN
but I found the format of the images is important too and I don't know between JPG, Webp, and PNG which one is better fit in this situation for optimizing. how can I choose between them?

PHP: How to compress images without losing visible quality (automatically)?

I'm wondering how to figure out the best compress rate (small filesize + no quality loss) automatically.
At the moment I'm using imagejpeg() with $quality = 85 for each .jpg.
PageSpeed (Chrome Plugin) suggests, to lower the quality of a few images to save some kb. The percentage of reduction is different.
I'd like to write a cronjob that crawls a specific directory and optimizes every image.
How does PageSpeed or TinyPNG figure out the best optimized quality and is this possible with PHP or another serverside-language?

TinyPNG uses pngquant.
Pngquant has option to set desired quality, similar to JPEG. You can run something like:
<?php system('pngquant --quality=85 image.png'); ?>
Pngquant website has example code showing how to use pngquant from PHP.
For JPEG you can apply lossless jpegcrush.
JpegMini (commercial) and jpeg-archive (free) are lossy and can can automatically find a minimal good quality for a JPEG.
In PHP you can roughly estimate how much JPEG was compressed by observing how much file size changes after re-compression. File size of JPEG recompressed at same or higher quality will not change much (but will lose visual quality).
If you recompress JPEG and see file size halved, then keep the recompressed version. If you see only 10-20% drop in file size, then keep the original.
If you're compressing yourself, use MozJPEG (here's an online version).

Determine DPI for an Image with PHP

What is the fastest and easiest way to determine the DPI of an image in PHP using either ImageMagick or GD? Although it would be nice to determine the DPI of a wide variety of formats, at the very least, JPEG and PNG should be supported.
Similar questions:
How to Check Photo DPI with PHP
JPEG only solution

Compress images with PHP

I process uploaded images by php to save (after resize) by imagejpeg. As I explored, imagejpeg is the best php command to compress jpg images to reduce the file size. However, when I check my website by Google Page Speed, it says all of my images can be compressed 4-10%.
What is the common method to compress images to meet the Google standard?

Googles "standard" is the possible maximum to be expected by google. You need to use highly optimized image compressors that does nothing else than image compressing and therefore get a possible maximum best value here.
You can for example, open you jpeg file in a image editor like adobe photoshop and create the possible maximum best compression to be expected by you while having visual control. Highly recommended.
The GD library provides a standard conform jpeg compression which should match a library users expectation, but which might not satisfy a graphic designer (and/or google by 4-10%).

layered png image using a PHP library

Does anyone know about a PHP library which can produce layered PNG images? (I'm not sure, but I think that tiff image standard supports layers also)

AFAIR, PNG does not support layers. MNG does and you can produce these with ImageMagick. For PHP extension see: http://www.php.net/imagick

From the ImageMagic API site:
PHP
MagickWand for PHP a native PHP-extension to the ImageMagick MagickWand API.
IMagick is a native PHP extension to create and modify images using the ImageMagick API. Documentation for the extension is available here.
phMagick is a wrapper class for ImageMagick, wrapping the most common web image manipulation actions in easy to use functions, but allowing full access to ImageMagick's power by issuing system calls to it's command-line programs.
ImageMagick® is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD, PNG, Postscript, SVG, and TIFF. Use ImageMagick to translate, flip, mirror, rotate, scale, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves.

Assuming you mean the layered PNG files as per fireworks, I don't think you can do it. I've not seen anything except fireworks that supports these files properly.

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